Scroll-type fluid displacement devices which are generally known as scroll pumps, compressors, and expanders, is well know in the art. In U.S. Pat. No. 801,182, issued to Creus, it is disclosed the basic construction of a scroll type fluid displacement apparatus which comprises a pair of scrolls each having a circular end plate and a spiroidal or "involute" spiral element. The scrolls are maintained angularly and radially offset with respect to each other so that both spiral elements interfit to form a plurality of line contacts between their spirally curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motions the two scrolls shifts the line contacts along the spirally curved surfaces and change the volume of the fluid between the spiral elements. Scroll type fluid displacement apparatus may be used to compress, expand or pump fluids.
One of the most common applications of scroll type fluid displacement apparatus is for use as refrigerant compressors in refrigerators and/or all conditioning units. In a typical scroll-type refrigerant compressor, which comprises an orbiting scroll member and a stationary scroll member, refrigerant gas is taken into fluid pockets formed at the outer most end of the spiral element. Due to the orbital motion of the orbiting scroll member, the fluid pockets are gradually compressed as they are moved toward the center of the spiral elements. Finally, when compressed fluid reaches the central portion of the interfitting spiral elements, the compressed fluid is discharged to an external fluid circuit and exits the system.
The scroll-type compressor potentially has the advantages of offering quiet, efficient, and low-maintenance operation in a variety of refrigeration applications application. However, several design and manufacturing problems have persisted since the inception of the scroll-type compressors which have hindered the scroll compressors from achieving the wide market acceptance and commercial success as expected. Some of the more notable problems include the difficulty and high cost of fabricating the fixed and orbiting scroll members. These problems make it less competitive against other types of compressors such as reciprocating piston and rotary vane type compressors.
There are two basic constructional alternatives for fabricating scroll members, namely, the single-piece process which involves forming the end plate and the involute wrap as an integral member (e.g., by machining out the involute wrap), or the two-piece process which involves forming the involute wrap and the end plate separately and then joining them into a finished scroll member. The single-piece process provides superior mechanical integrity of the scroll members. However, fabricating an integrally formed scroll member using the single-piece process requires excessive amounts of time and man-power; it also generates large quantities of waste metal. Several methods which involve the steps of forming separate pieces then joining the involute wrap and the end plate together have been proposed; however, none appears to have proven economic feasibility or satisfy many of the stringent technical and precision requirements of modern day refrigerant compressors, such as high precision, dimensional stability, and abrasion resistance, to name a few.
U.S. Pat. No. 4,403,494 discloses a method and apparatus for forming scroll members containing an end plate and an involute wrap rigidly affixed to the end plate. In the method disclosed in the '494 patent, the end plate and the involute wrap are precision formed by casting either as an integral element or as two separate elements and then the scroll member is coined to the desired dimensional accuracy. This procedure is applicable only to those wrap metals having sufficient ductility to permit it to be precisely coined to the desired configuration. The requirement for good ductility often causes surface resistivity (particularly resistance to abrasion) to be compromised. To ameliorate this weakness, it was suggested that an additional step be provided which involves temporarily masking the flank surfaces of the wrap and then treating the end plate surface by hard anodization or by hard chrome plating.
U.S. Pat. No. 5,051,079 discloses a scroll-type hermetic compressor having a fixed scroll member assembly and an orbiting scroll member assembly within a hermetically sealed housing. Each of the fixed and orbiting scroll member assemblies includes a separately formed scroll wrap member interconnected with a plate member. The wrap member is affixed to the plate member by the retention of the axial end thereof within a matching involute channel in the plate member by a welded joint, a sintered joint, a press fit, or an interference fit. The wrap member is disposed within the channel such that the axial end surface thereof is essentially flush with the back surface of the plate member. The plate member of the fixed scroll member assembly is mounted to a frame member, and the plate member of the orbiting scroll member assembly is mounted to a drive hub member.
U.S. Pat. No. 4,627,800 discloses a scroll type fluid displacement compressor with spiral wrap elements of varying thickness. The fluid displacement compressor includes a pair of scrolls each having a circular end plate and a spiral element extending therefrom. The scrolls are maintained at an angular and radial offset so that the two spiral (i.e., wrap) elements interfit so as to form a plurality of line contacts which define at least one pair of sealed off fluid pockets. Upon relative orbital motions of the scrolls, the line contacts shift along the spirally curved surfaces of the spiral elements to change the volume of the fluid pockets. In the scroll type fluid displacement compressor disclosed in the '800 patent, the thickness of the spiral element of the orbiting scroll is gradually reduced from the inner end of the spiral element to its outer end to increase the mechanical strength of the spiral element at its central portion. The thickness of the spiral element of the fixed scroll is, on the other hand, gradually increased from the inner end of the spiral element to its outer end to compensate for the change in the shape of the facing spiral element of the orbiting scroll.
U.S. Pat. No. 4,838,936 discloses a method for making forged aluminum alloy spiral parts, such as orbiting and fixed scroll plates having involute wraps, for use in making scroll compressors. This method includes the steps of first forming a preform (green compact) from aluminum alloy powder, such as Al-20Si, Al-35Si, etc., having fine and homogeneous microstructures as raw material by compressing with a die assembly and cold isostatic pressing. Then the aluminum alloy preform is hot-forged to produce the spiral parts.
U.S. Pat. No. 4,512,066 discloses a method for fabricating scroll members comprising the steps of (1) forming a precision pre-formed scroll member having an involute wrap affixed to an end plate; the inner and outer flanks of the involute wrap are joined to the end plate along the base of the involute wrap; (2) forming re-entrant corners between the surface of the end plate and the inner and outer flank surfaces; and (3) broaching the inner and outer flanks of the involute wrap axially toward the surface of the end plate to attain a pre-determined thickness of the involute wrap and a radial spacing between the turns thereof. The re-entrant corners provide clearance for chips resulting from the broaching step. In the process disclosed by the '066 patent, the pre-formed scroll member is formed as an integral element containing both the involute wrap and the end plate by die casting.
U.S. Pat. No. 5,044,904 discloses a hermetically sealed compressor having a fixed scroll member assembly and an orbiting scroll member assembly within a hermetically sealed housing. Each of the fixed and orbiting scroll member assemblies includes a separately formed scroll wrap member interconnected with a plate member by means of a plurality of interconnecting pin members received within corresponding axial bores in the wrap member and the plate member. The plate member of the fixed scroll member assembly is mounted to a frame member, and the plate member of the orbiting scroll member assembly is mounted to a drive hub member operably coupled to a crankshaft. In the scroll member assembly disclosed in the '904 patent, the interconnecting pin members fit loosely within the bores in the wrap member such that the wrap member is movable with respect to the plate member thereby providing radial compliance between the fixed and orbiting scroll member assemblies during compressing operations.
U.S. Pat. No. 4,802,831 discloses a compressor comprising stationary and orbiting scroll members. The stationary and orbiting scroll members are formed thereon with spiral wraps engaged with each other to define compression chambers which, when the orbiting scroll member is moved relative to the stationary scroll member, are radially inwardly moved which decreasing their volumes. Each scroll member is composed of a metallic base scroll member and a spiral wrap formed on one side of the metallic base scroll member. The surface of the metallic base member and the spiral wrap are provided with a coating layer of a resin composition. The resin composition comprises a thermosetting resin and an inorganic filler and has a linear thermal expansion coefficient of not greater than 2.8.times.10 .sup.5 cm/cm/.degree.C. and a glass transition temperature of not lower than 160.degree. C.